The present invention relates to a system for the yaw control of an aircraft, in particular a civil airliner.
The Applicant""s patent FR-2 617 120 discloses a system for the roll and yaw control of an aircraft, implementing electric flight controls.
As regards in particular the yaw control, this known system comprises:
a control facility (rudder bar), for the yaw control, capable of being actuated by a pilot of the aircraft;
a transducer delivering electrical signals PE depending on the position of said control facility and representative of a controlled direction;
first means delivering electrical signals representative respectively of the controlled roll attitude "PHgr"c, of the roll rate p, of the effective roll attitude "PHgr", of the yaw rate r and of the sideslip xcex2 of said aircraft;
a computation unit formulating:
an electrical command dr for yaw control, on the basis of the relation:
dr=Ka."PHgr"c+Kb.p+Kc."PHgr"+Kd.r+Ke.xcex2
xe2x80x83in which:
"PHgr"c, p, "PHgr", r and xcex2 are the values delivered by said first means, and
Ka, Kb, Kc, Kd and Ke are gains, the values of which are capable of being fixed by second means at nominal values; and
an electrical command dpequi for roll control (required to be transmitted to ailerons and spoilers of said aircraft), on the basis of the relation:
dpequi=ka1."PHgr"c+kb1.p+kc1."PHgr"+kd1.r+ke1.xcex2+kf.PE,
xe2x80x83ka1, kb1, kc1, kd1, ke1 and kf being gains; and
a transmission device, of mechanical type, making it possible to combine said electrical command dr for yaw control and a mechanical command which originates directly from the control facility by way of a mechanical transmission and which is representative of the position of said control facility, so as to deliver a single combined command for yaw control which is intended to control a rudder of the aircraft.
This standard yaw control system presents numerous advantages and, in particular, it makes it possible to reduce the workload of the pilot. Moreover, it makes it possible to ensure:
good damping of the Dutch roll;
good coordination between roll and yaw, especially by taking into account the controlled and effective roll attitudes and the roll rate when computing the electrical command dr for yaw control; and
proper behavior of the aircraft on takeoff.
However, the effectiveness of this known system can be improved in the case of a fault with one of the engines of the aircraft, in particular as regards the yaw/roll control, this being especially so in unsteady flight configurations of the aircraft, that is to say those for which lift-augmenting means, such as lift-augmenting flaps, envisaged for landing and takeoff, are activated.
Moreover, one is aware that it is recommended, with control systems of this type, in the case of a fault with an engine in the approach phase, to carry out approach maneuvers without using the autothrottle. Indeed, when the autothrottle is engaged, the yaw torque induced by the thrust variations of the unfaulty engine or engines disturbs the behavior of the aircraft and increases the workload of the pilot, instead of reducing it.
The object of the present invention is to remedy these drawbacks. It relates to an aircraft yaw control system, which makes it possible to improve the yaw control in the case of a fault with an engine, in particular in the takeoff and landing phases, whilst maintaining close to nominal behavior of the aircraft, especially on takeoff.
For this purpose, according to the invention, the yaw control system, of the aforesaid type, for an aircraft fitted with a plurality of engines is noteworthy in that it moreover comprises third means for detecting any fault with one of said engines of the aircraft, and in that said second means are formed in such a way as to increase the value of the gain Kd relating to the yaw rate r and to modify the values of the gains Ka and Ke relating respectively to the controlled roll attitude "PHgr"c and to the sideslip xcex2, upon the detection by said third means of a fault with an engine of the aircraft.
Thus, according to the invention, when there is a fault with an engine, the gains relating to the controlled roll attitude and to the sideslip are modified and the gain relating to the yaw rate is increased, so that said control system issues a rudder deflection command, which is correspondingly greater the higher the yaw rate and/or the sideslip and which thus makes it possible to counter, effectively and automatically, any disturbance in terms of yaw and slip, induced by the fault with the engine, thus making it possible to remedy the aforesaid drawbacks.
Moreover, in order to obtain roll behavior similar to the nominal lateral law, advantageously, said second means are formed in such a way as to modify the values of the gains Ka1 and Kf of the electrical command dpequi for roll control, relating respectively to the controlled roll attitude "PHgr"c and to the controlled direction, upon the detection by said third means of a fault with an engine of the aircraft, in such a way as to allow the aircraft to maintain the same roll behavior despite the fault.
The control system in accordance with the invention presents other advantages and, in particular, it ensures:
homogeneity in all flight phases;
preservation of the standard piloting procedures and maneuvers, that is to say it does not modify the piloting; and
reliable implementation, which is independent in particular of the speed of the aircraft or of the magnitude of the asymmetry induced by the fault with an engine.
Furthermore, advantageously, the control system in accordance with the invention comprises fourth means for determining the current flight configuration of the aircraft.
Additionally, advantageously, said third means are formed in such a way as to detect a fault with an engine, for an aircraft fitted with two engines:
condition 1: if the parameter N1 (rate of rotation of the low pressure module) of an engine is greater than a predetermined value and if the difference of the parameters N1 of the two engines is greater than a predetermined value, this making it possible to detect a fault with an engine in the takeoff phase; and
condition 2: if the difference of the parameters N1 of the two engines is greater than a predetermined value and if a second characteristic condition is satisfied, for example the parameter N2 (rate of rotation of the high pressure module) of said engine is less than a predetermined value, an engine is idling, a fuel supply is cut off or an engine monitoring system is not switched on, this making it possible to detect a fault with an engine in the approach phase or the takeoff phase.
According to the invention, said second means carry out a modification, in particular an increase, of the values of the gains as a function of the current flight configuration of the aircraft. For this purpose, preferred values of the gains will be specified hereinafter as a function of various possible flight configurations.
Moreover, preferably, the system in accordance with the invention comprises means of priority action which are formed in such a way as to act on said second means so that the latter modify the values of the aforesaid gains, in the case of a fault with an engine, only when the aircraft is in flight and when it is in an unsteady flight configuration.
Furthermore, advantageously, said second means are formed in such a way as to remodify the values of the gains, modified previously following a fault with an engine, so as to return to said nominal values, at least when one of the following conditions is realized:
the aircraft switches to a steady configuration;
the engine initially faulty is no longer so and all the xe2x80x9cenginexe2x80x9d controls of the aircraft have no longer been idling for at least a predetermined duration; and
for an altitude of the aircraft which is less than a predetermined altitude, the previously faulty engine is so only in respect of aforesaid condition 2 and not in respect of aforesaid condition 1, and the position of said control facility exceeds a predetermined position.
It will be noted that, through the amplifying action in accordance with the invention, the rudder is swung much harder and responds more swiftly to any variation in yaw and/or in slip. Also, for reasons connected with both comfort and the fatigue of said rudder, the amplifying action envisaged by the present invention is employed, preferably, only in the case of a fault with an engine, and in respect of the phases of flight with an unsteady configuration, that is to say on takeoff and on landing.
Additionally, in order to accommodate a dual objective in the approach phase, namely, on the one hand, to preserve control in respect of the action of the control facility, in particular to make it possible if necessary to return the speed vector of the aircraft to the axis of the latter, and, on the other hand, to maintain the amplifying action in accordance with the invention down to the ground, in particular so as not to disturb the pilot on landing, advantageously, second means are formed in such a way as to remodify, progressively, the values of the gains Kd and Ke, previously modified following a fault with an engine, so as to return to said nominal values, when the following conditions are simultaneously realized:
the aircraft is at an altitude which is less than a predetermined altitude;
the position of said control facility lies outside a predetermined range of positions; and
only the aforesaid condition 2 is true (no condition 1).
Within the framework of the present invention, in order to ascertain whether the aircraft is or is not beneath said predetermined altitude, it is of course possible to measure its effective altitude directly, for example by means of radioaltimeters. However, other available information such as the position of the slats and of the flaps or the position of the landing gear may also be used for this purpose, in a complementary manner or as a variant.
Furthermore, especially for reasons of comfort, advantageously, the second means are formed in such a way as to modify, that is to say to increase and/or to lower, always progressively the values of the various gains, required to be modified upon implementation of the present invention.